Method of preparing purified phosphates
from impure phosphoric acid

ABSTRACT

EMBODIMENT NO. 1: PURFIED ALKALI METAL OR ANNONIUM ORTHOPSPHATES ARE PREPARED BY ADDING MELAMINE TO IMPURE WET-PROCESS PHOSPHORIC ACID TO FORM CRYSTALS OF INSOULBLE MELAMINE ORTHOPHOSPHATE WHICH ARE SEPARATED FROM THE MOTHER LIQUOR AND CAUSED TO REACT WITH AN AQUEOUS SOLUTION OF ALKALI METAL OR AMMONIUM HYDROXIDE A SALT THEEREOF WITH AN UNSTABLE VOLTABLE ANION WHICH IS ENVELOPED AS A GAS FROM THE SOLUTION, THEREBY FORMING CRYSTALS OF MELAMINE FOR RECYCLE AND A SOLUTION OF THE DESIRED PURIFIED ORTHOPHOSPHATE. EMBODIMENT NO.2: ALKALI METAL OR AMMONIUM PYROPHOSPHATES ARE PREPARED BY HEATING MELAMINE ORTHOSPHOSPHATES (PREPARED AS FOR EXAMPLE IN AMBODIMENT NO. 1 SUPRA) AT 200* TO 300* TO CONVERT IT TO MELAMINE PYROPHOSPHATE AND ALLOWING IT TO REACT WITH AN AQUEOUS SOLUTION OF ALKALI METAL OR AMMONIUM HYDROXIDE OR A SALT THEREOF CONTAINING AN UNSTABLE VOLATILE ANIOM WHICH IS EVOLVED AS A GAS FROM THE SOLUTION, THEREBY FORMING CRYSTALS OF MELAMINE FOR RECYCLE AND A SOLUTION OF THE DESIRED PYROPHOSPHATE. RELATIVELY PURE PYROPHOSPHATE ARE OBTAINED FROM IMPURE WET-PROCESS ORTHOPHOSPHORIC ACID.

DEFENSIVE PUBLICATION UNITED STATES PATENT OFFICE Published at the request of the applicant or owner in accordance with the Notice 0! Dec. 16, 1989, 869 0.6. 687. The abstracts of Defensive Publication applications are identified by distinctly numbered series and are arranged chronologically. The heading of each abstract indicates the number of pages of specification, including claims and sheets or drawings contained in the application as originally filed. The files of these applications are available to the public for inspection and reproduction may be purchased for 30 cents a sheet.

Defensive Publication applications have not been examined as to the merits of alleged invention. The Patent Oflice makes no assertion as to the novelty or the disclosed subject matter.

PUBLISHED APRIL 23, 197i 921 O.Gr. 1307 T921 024 METHOD OF PREPARlNdPURIFIED PHOSPHATES FROM IMPURE PHOSPHORIC ACID Richard C. Sheridan, 105 Terrace, Sheflield,

' Ala. 35660 Filed Feb. 23, 1973, Ser. No. 335,377

Int. Cl. C01b 33/12 US. Cl. 423-305 3 Sheets Drawing. 15 Pages Specification Embodiment No. 1: Purified alkali metal or ammonium orthophosphates are prepared by adding melamine to impure wet-process phosphoric acid to form crystals of insoluble melamine orthophosphate which are separated from the mother liquor and caused to react with an aqueous solution of alkali metal or ammonium hydroxide or a salt thereof with an unstable volatile anion which is evolved as a gas from the solution, thereby forming crystals of melamine for recycle and a solution of the desired purified orthophosphate.

Embodiment No. 2: Alkali metal or ammonium pyrophosphatcs are prepared by heating melamine orthophosphate (prepared as for example in embodiment No. 1 supra) at 200 to 300 to convert it to melamine pyrophosphate and allowing it to react with an aqueous solution of alkali metal or ammonium hydroxide or a salt thereof containing an unstable volatile anion which is evolved as a gas from the solution, thereby forming crystals of melamine for recycle and a solution of the desired pyrophosphate. Relatively pure pyrophosphates are obtained from impure wet-process orthophosphoric acid.

Apnl 2 3, 1974 R. c. SHERIDAN T921,024

. METHOD OF PREPARING PURIFIED PHOSPHATES FROM-IMPURE PHOSPHORIC ACID Filed Feb. 215, 1973 5 Sheets-Sheet 1 RECYCLE WET- PROCESS MELAMINE H3PO4 REACTOR MELAMINE PHOSPHATE (SLURRY) IMPURE H3PO4 Fl LTRATE MELAMINE PHOSPHATE (CAKE) l NH3 H20 3 NEUTRALIZER MELAMINE (SLURRY) IN SOLUTION OF AMMONIUM PHOSPHATE 1 A FILTER KV MELAMINE SOLUTION OF PURIFIED PHOSPHATE CRYSTA LLIZER CRYSTALLINE DIAMMONIUM HYDROGEN ORTHOPHOSPHATE (NH4)2 HPO4 PREPARATION OF AMMONIUM PHOSPHATE BY MELAMINE RECYCLE April 23, 1974 R.- C. SHERIDAN Pi 1w! Feb 215, 1973 RECYCLE MELAMINE 6 Sheets-Sheet :3

WET- PROCESS MELAMINE REACTOR MELAMINE PHOSPHATE (SLURRY) v /6 FILTER IMPURE H3PO4 FILTRATE MELAMINE PHOSPHATE (CAKE) CALCINER H o MELAMINE PYROPHOSPHATE NH3+ H20 /a NEUTRALIZER MELAMINE (SLURRY') IN SOLUTION OF (NH4)4P2O7 /9 FILTER (NH4)4P2O7 20 l CRYSTALLIZER CRYSTALLINE TETRAAMMONIUM PYROPHOSPHATE (NH4)4P2O7 Fig. 2

PREPARATION OF AMMONIUM PYROPHOSPH ATE BY MELAMINE RECYCLE P 23, 1974 R. c. SHERIDAN T92l,024

METHOD OF PREPARING PURIFIED PHOSPHATES FRO! IMPURE PHOSPHORIC ACID Filed Feb. 23, 1973 3 Sheets-Sheet 3 2. O I l (5 I70C E Z 2 L6 2 L2] O I 2 P. D: O

31 A souo LINES,CALCULATED g 0,A,|J OBSERVED VALUES .-1

Q4 l I F ig. 3 RATE OF'CONDENSATION OF MELAMINE ORTHOPHOSPHATE I I I I I SOLID LINE, CALCULATED O OBSERVED VALUES ARRHENIUS PLOT OF CONDENSATION OF MELAMINE ORTHOPHOSPHATE 

